This method of using steel rods as the structure instead of foam is most ideal for thin objects such as swords and weapons. Fiberglass alone is very strong and light, but under long lengths it starts to flex a bit. By adding the steel as a skeleton, the length of the object becomes much stronger, yet also a bit heavier. And the thicker the fiberglass is, the greater the weight as well.
The same steps apply for this method as with the foam method. The only difference here, is that steel rods are used as the structure instead of foam, and the hardened fiberglass is what is carved into the desired shape rather than the foam.